Device for detecting the level of a medium

ABSTRACT

A capacitive level sensor device, for detecting the level of a medium contained in a container, comprises a circuit support, which extends longitudinally substantially according to level-detection axis. 
     The circuit support has, in a detection region thereof, at least one first plurality of first capacitive elements, which comprise at least one first array of first electrodes, preferably spaced from one another along the level-detection axis, which are arranged in a position corresponding to at least one first side of a supporting structure of the circuit support. 
     The sensor device has a casing body which comprises an electrically insulating and fluid-tight detection portion, which covers the detection region of the circuit support. The detection portion of the casing body comprises an overmoulded outer coating, made of a first electrically insulating polymeric material, which defines an outer surface of the casing body designed to be in contact with the medium the level of which has to be detected. 
     Between the overmoulded outer coating and the first electrodes there is set at least one intermediate layer made of an electrically insulating material different from the first material. The at least one intermediate layer comprises a layer made of a material selected from among materials that include silicon, or derivatives or compounds thereof, and materials that include fluorine derivatives or compounds.

This application is the U.S. national phase of International ApplicationNo. PCT/IB2018/055198 filed 13 Jul. 2018, which designated the U.S. andclaims priority to IT Patent Application No. 102017000082457 filed 20Jul. 2017, the entire contents of each of which are hereby incorporatedby reference.

DESCRIPTION Field of the Invention

The present invention relates to a sensor device for detecting the levelof a generic medium, such as a liquid, a fluid substance, a powderymaterial, or a material in the bulk state, etc. The invention has beendeveloped with particular reference to level sensors used on vehicles,preferably level sensors of a capacitive type.

Prior Art

A level-sensor device of the type referred to is known, for example,from WO 2015/181770 A, filed in the name of the present Applicant.According to a first embodiment, the device disclosed in WO 2015/181770has a hollow casing, which is to be immersed in the liquid undergoingdetection, partially housed within which is a circuit support or PCB(Printed-Circuit Board). The circuit support carries an array ofcapacitive detection elements, represented by metal electrodes that aresubstantially the same as one another and are arranged on the support ata distance apart from one another along a level-detection axis. Thehollow casing is configured as a distinct component, obtained viamoulding of a thermoplastic material, and subsequently inserted thereinis a corresponding portion of the circuit support, which carries thedetection electrodes. Then introduced in the cavity of the casing is anelectrically non-conductive fluid filling material, such as apolyurethane resin or a gel, preferably a silicone gel. The presence ofthe aforesaid fluid filling material is mainly aimed at preventing thepresence of gaps and air pockets within the cavity, in particular in themicro-cavities determined by the roughness in the area of contactbetween the circuit support, and/or corresponding electrodes, and thecasing, which could have an adverse effect on the level measurement(these concepts are clarified also by the details represented in FIGS.14 and 15 of the document cited, from which it is evident that thesupport and/or the electrodes is/are in contact with the casing, and theaforesaid fluid filling material does not form an insulating layer).

The above embodiment of the device has as a consequence that theproduction process must necessarily envisage prior arrangement of thehollow casing, as well as certain specific operations for insertion ofthe circuit support in the hollow casing and certain specific operationsfor introduction of the fluid filling material into the cavity of thecasing (in addition, obviously, to management of the supplies andmovement of the casing bodies and of the filling material).

According to a second embodiment, WO 2015/181770 envisages replacementof the aforesaid hollow casing with an outer coating, formed by directovermoulding of plastic material on the circuit support. This type ofsolution simplifies production of the level-sensor device as a whole,but implies in time a decay of its precision of detection, followingupon the presence of humidity around the detection electrodes.

The present Applicant has in fact noted that, following upon use of thedevice, the overmoulded plastic material of the outer coating tends toabsorb humidity, on account of the practically constant contact with theliquid undergoing detection. This humidity, the negative effects ofwhich appear with the passage of time, leads to imprecisions ofdetection already in the course of the service life of the device. Thesame problem is present also in devices built according to the aforesaidfirst embodiment of WO 2015/181770, given that its hollow casing isconfigured for pressing the circuit support against a wall delimited bythe corresponding housing cavity so that the electrodes are in strictcontact with the wall, which is itself liable to absorb humidity intime.

The sensitivity of the capacitive measurement is maximum if a liquid isset on the surface of the detection electrode and decreases(substantially exponentially) as of the distance between the liquid andthe surface of the electrode increases linearly. The same behaviouroccurs, however, if, instead of the liquid, water vapour or humidity ingeneral is present. In other words, the presence of humidity in thematerial of the hollow casing or of the overmoulded coating, and henceon the electrodes in contact with the aforesaid material, has the effectof “emulating” the presence of liquid, thereby vitiating to a certainextent the level-sensing precision.

An overmoulded coating may be formed using a plastic material havinggood barrier properties and good properties of resistance to humidity.However, materials of this type are in general costly and difficult toprocess for the purposes of formation of the overmoulded coating (thesensing part of the device is in general rather long, which rendersdifficult the operation of overmoulding using certain polymers).

The present Applicant has moreover found that certain polymers thatpresent good barrier properties and good properties of resistance tohumidity have the drawback of presenting considerable shrinkage, and/ordimensional deformations following upon the moulding operations, and/oron account of expansion and thermal shock. This may cause faults in acircuit support (i.e., in the corresponding electrical paths, and/orelectrodes, and/or electronic components) on which such a polymer isdirectly overmoulded. In any case, also these materials are inevitablysubject to absorbing humidity in the long term, following upon prolongedcontact with the liquid undergoing detection.

On the other hand, the overmoulded coating may be obtained using othertypes of plastic materials (for example, certain thermoplasticpolymers), which are less expensive and more easily mouldable. Thesematerials in general present, however, poorer characteristics ofresistance to humidity, and hence a faster decay of the precision oflevel sensing by the device.

SUMMARY AND AIM OF THE INVENTION

In view of what has been set forth above, the object of the presentinvention is to provide a capacitive level-sensor device that is builtin a simple and economically advantageous way, but is distinguished byan increased precision, sensitivity, and reliability of detection in thelong term, as compared to known devices designed for similarapplications. The above and other aims still, which will emerge moreclearly hereinafter, are achieved according to the invention by alevel-sensor device having the characteristics specified in the annexedclaims. The claims form an integral part of the technical teachingprovided herein in relation to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aims, characteristics, and advantages of the invention willemerge from the ensuing description, with reference to the annexeddrawings, which are provided purely by way of non-limiting example andin which:

FIG. 1 is a perspective sectioned view of a generic container thatcomprises a level-sensor device according to possible embodiments of theinvention;

FIG. 2 is a partially sectioned schematic perspective view of alevel-sensor device according to possible embodiments of the invention;

FIG. 3 is a schematic longitudinal section of a level-sensor deviceaccording to possible embodiments of the invention;

FIGS. 4 and 5 are schematic views, respectively a perspective view and afront elevation, of a level-sensor device according to possibleembodiments of the invention;

FIGS. 6 and 7 are schematic cross-sectional views according to the linesVI-VI and VII-VII, respectively, of FIG. 5;

FIGS. 8-12 illustrate, via schematic perspective views, a possiblesequence of assembly of a level-sensor device according to possibleembodiments of the invention;

FIGS. 13 and 14 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 15 and 16 are schematic cross-sectional views according to thelines XV-XV and XVI-XVI, respectively, of FIG. 14;

FIGS. 17 and 18 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 19 and 20 are schematic cross-sectional views according to thelines XIX-XIX and XX-XX, respectively, of FIG. 18;

FIGS. 21 and 22 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 23 and 24 are schematic cross-sectional views according to thelines XXIII-XXIII and XXIV-XXIV, respectively, of FIG. 22;

FIGS. 25 and 26 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 27 and 28 are schematic cross-sectional views according to thelines XXVII-XXVII and XXVIII-XXVIII, respectively, of FIG. 26;

FIGS. 29 and 30 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 31 and 32 are schematic cross-sectional views according to thelines XXXI-XXXI and XXXII-XXXII, respectively, of FIG. 30;

FIGS. 33 and 34 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 35 and 36 are schematic cross-sectional views according to thelines XXXV-XXXV and XXXVI-XXXVI, respectively, of FIG. 34;

FIGS. 37 and 38 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention;

FIGS. 39 and 40 are schematic cross-sectional views according to thelines XXXIX-XXXIX and XL-XL, respectively, of FIG. 38;

FIGS. 41 and 42 are schematic cross-sectional views similar to those ofFIG. 39, regarding level-sensor devices according to further possibleembodiments of the invention;

FIGS. 43 and 44 are schematic views similar to those of FIGS. 4 and 5,regarding a level-sensor device according to further possibleembodiments of the invention; and

FIGS. 45 and 46 are schematic cross-sectional views according to thelines XLV-XLV and XLVI-XLVI, respectively, of FIG. 44.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Reference to “an embodiment”, “one embodiment”, or “various embodiments”and the like, in the framework of the present description is intended toindicate that at least one detail, configuration, structure, orcharacteristic described in relation to the embodiment is comprised inat least one embodiment. Hence, phrases such as “in an embodiment”, “inone embodiment”, “in various embodiments”, and the like, that may bepresent in various points of the present description do not necessarilyrefer to one and the same embodiment, but may instead refer to differentembodiments. Moreover, particular conformations, structures, orcharacteristics defined in this description may be combined in anyadequate way in one or more embodiments, even different from the onesrepresented. The reference numbers and spatial references (such as“upper”, “lower”, “top”, “bottom”, “front”, “back”, “vertical”, etc.)used herein, in particular with reference to the examples in thefigures, are provided merely for convenience and hence do not define thesphere of protection or the scope of the embodiments. In the presentdescription and in the attached claims, the generic term “material” isto be understood as including also mixtures, compositions, orcombinations of a number of different materials. In the figures, thesame reference numbers are used to designate elements that are similaror technically equivalent to one another.

In FIG. 1, designated as a whole by 1 is a generic container of ageneric substance, in particular a tank of a motor vehicle. Thecontainer may, for example, be a tank that is to contain a liquid, forexample a fuel, or water, or an additive. In various embodiments, thecontainer 1 (defined hereinafter for simplicity also as “tank”) isdesigned to contain water required for operation of a system of aninternal-combustion engine, or else an additive or reducing agentrequired for the operation of a system for the treatment of the exhaustgases of an internal-combustion engine. Such a system served by the tank1 is designated by 2. The treatment system 2 may, for example, be an ADI(Anti-Detonant Injection) system, in which case the tank 1 will containwater, or else an SCR (Selective Catalytic Reduction) system, in whichcase the tank 1 will contain a solution of urea in aqueous solution,such as the one commercially known by the name AdBlue™. In both cases,the liquid is liable to freeze when the tank 1 is exposed to lowtemperatures (indicatively temperatures lower than 0° C.). For thisreason, the tank 1 may be equipped with a heater device. The container 1could, however, be used for other purposes, and/or in sectors differentfrom the automotive one, and could be designed to contain a differentsubstance.

The main body 1 a of the tank 1 may be made of any material, inparticular a material that is chemically resistant to the substancecontained and, prefereably, elettrically insulating, for example asuitable plastic material according to known technique, such as ahigh-density polyethylene (HDPE). To the tank 1 there may possibly beassociated a heater of a type in itself known, used for heating the tankitself, and/or its contents, for example in the event of freezing. Anelectrical heater is represented schematically in the figures by theblock designated by EH. In various embodiment, one such heater isassociated to, or integrated in, a sensor device in accordance with theinvention.

In the schematic example illustrated, the tank 1 has an upper part 3,for example an upper wall thereof, where an opening 3 a is provided fortopping-up of the liquid substance. A lower part 4 of the tank 1, forexample, a bottom wall thereof, has an outlet opening 5, via which thesolution exits or is drawn out, for example via a pump, for supplyingthe liquid to the system 2. Also at tle lower part 4, the tank 1 has asecond opening, designated by 6, at which the body of a sensor deviceaccording to various possible embodiments of the invention is sealinglyfixed. In various preferred embodiments, in fact, a sensor deviceaccording to the invention is to be installed in the lower part of ageneric container, in such a way that an outer surface of its body is atleast partly in contact with the liquid substance, also when thissubstance has a very low level in the container.

The sensor device, designated as a whole by 10, includes alevel-detection part 11, designed to extend at least partly inside thetank 1, in particular according to a level-detection axis X, which ispreferably substantially vertical (but, if need be, it may be inclinedwith respect to the vertical). Preferentially, a proximal end region ofthe detection part 11 extends inside the tank 1 at a height relativelyclose to the bottom wall 4 in order to be able to detect the presence ofan even very low level of liquid in the tank. It should be noted that,rather than directly mounted at the opening 6 of the tank 1, the device10 according to the invention may form, or be associated to, or beintegrated in, a further body or component that is sealingly at adifferent opening of the of the tank 1, for example a component thatcomprises at least one from among a heater and a pump, possibly shapedto obtain walls of a second container which extends inside the thank 1and is uitabl eto contain a part of the liquid present in the tank 1, oa component or module of the type known in the sector as .UDM (UreaDelivery Module), or else a component designed to prevent suddenvariations of the level of the liquid during movement of the vehicle.

In FIGS. 2 and 3, a device 10 according to possible embodiments isrepresented in isolation, via a perspective view partially sectioned anda view in longitudinal section. The device 10 has a casing body thatcomprises at least one detection portion 14, which is electricallyinsulating and fluig-tight and which prevalently belongs to thedetection part 11 of the device 10 (FIG. 1).

In various embodiments, the casing body of the device also comprises:

a connection and/or control portion 15 (hereinafter referred to forsimplicity as “connection portion”), for electrical connection of thedevice 10 to an external system, for example, a control unit belongingto the system 2 of FIG. 1, and

a mounting portion 16, which is configured for sealed coupling and/orpositioning of the device 10 on a different device, for example at theopning 6 of the tank of FIG. 1.

In various embodiments, the connection and/or control portion 15includes a generally hollow connector body 15 a, extending in which arerespective portions of electrical terminals, partially visible in FIG.3, where they are designated by 17. In various embodiments, theterminals 17, for example obtained via stamping or blanking from metalstrap, form, with the connector body 15 a, an interface for externalconnection of the device 10, for example to the aforesaid control unitof the system 2. Preferentially, each terminal 17 has a contact portion,preferably a lamina portion, designed for being positioned within thecavity of the connector body 15 a, and an interconnection portion, whichis preferably narrow, designed for electrical and mechanical couplingwith respective contact elements, for example present on a circuitsupport or substrate described hereinafter.

In various embodiments the mounting portion 16 extends axially betweenthe detection portion 14 and the connection and/or control portion 15and has, at an outer peripheral surface thereof, at least one seat 19 afor an annular sealing element, such as an o-ring gasket, which mayperforms possibly also function of elastic mounting of the device 10,for example with respect to the tnak 1 onto which theg device ismounted.

It should be noticed that, in various embodiments, particularly those inwhich a sensor device ina accordance with the invention is integrated ordesigned to be coupled with a different functional component (such asfor example an UMD module or an ADI module), the detection portion 14may belong to a housing body of such a functional component, whereas theconnection portrion 15 and/or the mounting portion 16 may be omitted, orat least in part defined by the housing body of the aforesaid functionalcomponent.

Partially visible in FIGS. 2 and 3 is also a circuit support or PCB(Printed Circuit Board), designated as a whole by 20, which extends atleast in the detection portion 14 of the casing body of the device, andpreferably also in the mounting portion 16 and in the connection and/orcontrol portion 15.

In these figures, designated by 21, 22 and 23, are three body parts,which are to be joined together with interposition of a proximal endportion of the PCB 20.

In the example of FIG. 3, the parts 21 and 22 form at least partiallythe connection portion 15 of the casing body, with the part 21 thatpreferentially defines the connector body 15 a and integrates theelectrical terminals 17. Again with reference to the example shown inFIG. 3, the same part 21 forms, together with the part 23 and a part ofan overnoulded coating (30), at least one part of the mounting portion16. Portions 15 and 16 of the casing body of the device 10 could also beformed in some other way, for example with at least some of parts 21,22, 23 and/or of portions 15 and 16 made of the same material as theaforesaid overmoulded coating and/or as integral part of coating,thereby possibly comprising invetive characteristics described withreference to the detection portion.

The detection portion 14, and preferably but not necessarily at leastone part of the mounting portion 16, comprises/comprise an overmnouldedouter coating 30, which is made of a first electrically insulatingmaterial. This outer coating 30, i.e., the material that forms it,defines an outer surface of the casing body of the device 10, which isdesigned to be in contact with the medium or substance the level ofwhich has to be detected.

Provided on the PCB 20 is at least part of the necessaryelectrical-connection elements (such as leads or electrical paths),and/or of the electrical and/or electronic componentry necessary forlevel detection. The PCB 20 has a load-bearing structure, or supportingstructure, made of electrically insulating material, suitable forproducing printed circuits. In various embodiments, the PCB 20 is formedusing at least one composite material that includes glass fibres, i.e.,silicon oxide, preferably a composite material having a matrix of epoxyresin, in which glass fibres are included, where the glass fibres arearranged to form a sort of non-woven fabric impregnated with the resin.Materials that are preferred in this sense are for example FR4,vetronite, and similar electrically insulating composite materials, suchGRP (Glass-Reinforced Plastic). On the other hand, as will be seenhereinafter, not excluded from the scope of the invention is the use ofother materials for obtaining the supporting structure of the PCB 20,such as ceramic or polymer-based materials, not necessarily composites,and/or materials including silicon or its derivatives or compounds.

The PCB 20 extends longitudinally between two ends along thelevel-detection axis X and has a generally flattened shape, whichincludes two opposite major sides (designated by 20 a only in FIG. 8),which define between them a PCB thickness T (indicated only in FIG. 4),and two opposite longitudinal edges (designated by 20 b only in FIG. 8),which define between them a PCB width W (indicated only in FIG. 4).

In the PCB 20—represented in isolation in FIG. 8—it is possible toidentify a detection region 24, which belongs to the detection part 11of the device 10 and includes the distal end of the PCB itself, as wellas a second region 25, hereinafter also defined for simplicity as“control and/or connection region”, which includes the proximal end ofthe PCB. Between the two regions 24 and 25 there may possibly beprovided also an intermediate region, such as the one designated by 26in FIG. 8, in particular designed to be in a position corresponding tothe mounting portion 16 of the casing body of the device 10.

To the region 25 of the PCB 20 there may be associated at least part ofthe electrical and electronic processing and/or control componentry ofthe device 10, and associated thereto are the terminals 17 (FIG. 3) forexternal electrical connection of the device 10. Instead, associatedprevalently to the region 24 of the PCB 20 is the level-detectioncomponentry. More in particular, associated to the region 24 is at leastone first array of capacitive elements, which comprises at least onefirst series of first electrodes in a position corresponding to a majorside of the PCB (for example, the major side hereinafter identified by alayer 20 ₃ or a layer 20 ₁, according to the embodiment considered). Itshould be noted that phrases such as “in a position corresponding to amajor side” or “at a major side” used with reference to the electrodes,and present also in the sequel of the present description and in theattached claims, do not necessarily imply that the electrodes referredto are arranged on the outside of the aforesaid side, i.e., on an outerface thereof. In various preferred embodiments, in themselvesautonomously inventive, the PCB 20 is a PCB of a so-called multilayertype, i.e., a circuit support having a multilayer supporting structurethat comprises a plurality of layers of electrically insulatingmaterial, for example laminated on one another, with the aforesaidelectrodes that are arranged between two layers of electricallyinsulating material of the structure.

In traditional multilayer PCBs, defined on one or more of theintermediate layers are corresponding electrically conductive paths, andpossibly also other active and/or passive components of an electricalcircuit arrangement, which are then “enclosed” within the multilayerstructure, the paths and/or circuit components present on one layerbeing possibly electrically connected to paths and/or circuit componentspresent on another layer via so-called metallized “vias” or holes.

According to an inventive solution proposed herein, used in thelevel-sensor device is a multilayer PCB 20 that integrates inside it atleast one first array of first electrodes used for capacitive leveldetection, i.e., in such a way that at least one layer of the multilayerstructure of the PCB 20 is set between the aforementioned firstelectrodes and the overmoulded material of the outer coating. Such acase is exemplified in FIGS. 2-3, where some of the aforesaid firstdetection electrodes are designated by the letter “J” (in FIG. 8 theseelectrodes are not visible in so far as they are covered by an outerlayer 20 ₃ of the PCB 20). According to variants not represented, thevarious configurations described with reference to multilayer circuitsupports or PCBs with internal electrodes could be obtained also in someother way, not necessarily envisaging a support with a number of layers,for example, envisaging a plurality of electrodes and electricallyconductive paths, such as shaped metal straps, then overmoulded with anelectrically insulating polymer that provides the supporting structurefor the electrodes and other circuit elements (conductive paths,metallized holes or vias, electrical and/or electronic components,etc.). As will be seen, in any case, according to other embodiments, thePCB 20 is preferably of a multilayer type, and/or its detectionelectrodes may be arranged on the outside of at least one of its sides,preferably at least one of its major sides.

In various embodiments, the electrodes J of the aforesaid first arrayare substantially the same as one another and are set at a distanceapart from one another along the level-detection axis X, in a predefinedand preferably homogeneous way. According to possible embodiments (notillustrated), however, one and the same array of capacitive elements mayalso include a number of different series of electrodes, the electrodesof one series having a geometry different from that of the electrodes ofanother series of the same array. In other embodiments, the electrodescould have a shape elongated in the direction of the level-detectionaxis X.

In various preferred embodiments the sensor 10 also comprises a secondarray of second capacitive elements on the detection region 24 of thePCB 20, wherein such a second array comprises at least one second seriesof second electrodes, preferably being substantially the same as oneanother, coplanar and spaced apart from each other along thelevel-detection axis X, and which are arranged in a positioncorresponding to the second major side of the PBC 20. Thischaracteristic can be appreciated for example from FIG. 3, wherein someof the aforesaid second electrodes are designated by

The invention will be described hereinafter with reference to the caserepresented, i.e., a PCB including two arrays of electrodes J and J₁:however, in accordance with non-represented embodiments, the PCB canincludes a single array of electrode, in a position corresponding to anyone of the sides thereof.

In the example shown in FIG. 3, the first electrodes J and the secondelectrodes J₁ are in substantially mirrored or mutually-alignedpositions (i.e., non staggered positions), with reference to the twoopposite major sides of the PCB 20: however, in other embodiments notrepresented herein, the second electrodes J₁ are in staggered positionswith respect to first electrodes J, with reference to thelevel-detection axis X: variants of this kind enable to increase theresolution of measure of the level of the device 10; to this purpose, itis preferable that the electrodes J₁ extend in intermediate positionswith respect to the electrodes J, and vice-versa, such that electrodesJ₁ enable to detect levels which are intermediate to those detectable bythe dei electrodes J.

In various embodiments the electrodes J and J₁ are connectedindividually to respective inputs of a controller—representedschematically in FIG. 8, where it is designated by MC—that belongs tothe control circuitry and that, for example, is positioned in the region25 of the PCB 20. Not excluded, however, is the case of connection of anumber of electrodes J and/or J₁ in parallel to one another to one andthe same input of the aforesaid controller. Preferably, the electrodes Jand J₁ have geometrical shapes that are the same as one another, or elsehave different shapes but the same surface dimensions or, in general,have the same electrical capacitance. The electrodes J and/or J₁ extendpreferentially in a direction transverse to the PCB 20 or to thelevel-detection axis X.

The electrodes J and J₁ are made of electrically conductive material,for example a metal material or a metal alloy. The electrodes J and J₁are preferably coplanar with respect to one another, within thecorresponding array, and may, for example, be in the form of plates orlaminas sunk in or applied on the supporting structure of the PCB 20, orelse may be constituted by an electrically conductive layer deposited onthe supporting structure of the PCB 20, for example using a silk-screenprinting technique or the like. In various embodiments, the PCB 20, orat least one of its layers, has vias or through holes containingelectrically conductive material, for electrical connection of theelectrodes J and J₁ together, and/or to corresponding conductiveconnection paths, and/or to possible other electrical and/or electroniccomponents present in the PCB 20.

The region 25 of the PCB 20 is preferably comprised between the proximalend of the PCB itself and the first electrode J or J₁ of thecorresponding array (in this perspective, the connection and/or controlregion 25 may hence include also the area corresponding to theintermediate region designated by 26 in FIG. 8). However, also includedin the scope of the invention is the case where electrical and/orelectronic control and/or processing components belonging to the circuitarrangement of the device 10 are arranged along the entire PCB 20 orwithin its detection region 24, i.e., in the proximity of, and/orbetween the electrodes J and/or J₁. In this perspective, the connectionand/or control region 25 may extend even substantially throughout thelength of the PCB 20, with a part thereof in common with the detectionregion 24. As has been said, in particular in the case of a PCB 20 ofthe type exemplified, i.e., having a multilayer structure, also at leastsome of the aforesaid electrical and/or electronic control and/orprocessing components may be arranged between two layers of electricallyinsulating material of the multilayer structure.

As already mentioned, in various embodiments, the components belongingto the measurement circuit arrangement that equips the device 10 includeat least one control unit or controller MC (for example, selected from,or comprising at least one from among, a microcontroller, amicroprocessor, a CPU, a DSP—Digital-Signal Processor, a memory, anintegrated circuit, an operational circuit, an A/D converter circuit, anelectronic switching circuit), as well as further active and/or passivecomponents (such as transistors, MOSFETs, resistors, capacitors, diodes,etc.).

In various embodiments, the controller MC has a plurality of inputs towhich the electrodes J and J₁ are connected individually, or else anumber of electrodes J and/or J₁ in parallel to one another areconnected to one and the same input of the controller MC. The controllerMC preferably comprises at least one processing logic unit, a memory,and inputs and outputs, amongst which inputs of an analog/digital type.The controller MC may, for example, be a microprocessor identified bythe code PIC16F1517 manufactured by Microchip Technology Inc. or amicroprocessor identified by the code of the series CY8C4200Mmanufactured by Cypress Semiconductor Corporation. The specificlevel-detection modalities implemented by the device 10 by means of theelectrodes J and/or J₁, of a capacitive type, may, however, be of anytype known in the sector, for example according to the teachings of anyof documents WO2015/181770, WO2016/042456, and WO2016/042459 filed inthe name of the present Applicant.

As has been mentioned, provided in the PCB 20 are electricallyconductive paths, for connection of various circuit elements, such asthe electrodes J and J₁, the possible further electrical and/orelectronic components, and the terminals 17 (some of these paths arerepresented schematically in FIG. 8 via dashed lines that depart fromthe controller MC). As has been said, the PCB 20 may present alsometallized vias or holes (represented schematically by dashed circles inFIG. 8), for connecting together different conductive paths, and/or forconnecting conductive paths and/or circuit components provided indifferent layers or parts of the PCB 20, to the outside world and/orinternally. As has been said, in fact, in various preferentialembodiments, the PCB 20 is a PCB with multilayer supporting structure,where the aforesaid paths may be provided on internal or intermediatelayers of the PCB itself.

In various embodiments, the sensor device according to the inventionincludes at least one further sensor means for detecting at least onefurther quantity different from the level of a substance. The furthersensor means may, for example, be selected from temperature sensors,pressure sensors, quality sensors, sensors designed to detectcharacteristics of composition and/or chemico-physical characteristicsof the fluid (such as an optical-type sensor). For instance, in variousembodiments, the circuit arrangement of the device 10 includes at leastone temperature sensor, in particular a sensor with temperature-variableelectrical resistance, such as a sensor of an NTC or PTC type. Such asensor may be mounted in a position corresponding to at least one fromamong the proximal end area, the distal end area, and an intermediatearea of the detection region 24 of the PCB 20. One such temperaturesensor is represented schematically by block TS in FIG. 8.

According to one aspect, the present invention proposes distancing orspacing apart the detection electrodes J or J₁ of a respectiove array(ar at least the surface thereof facing towards the medium the level ofwhich is to be measured) from the material that forms the overmouldedouter coating 30: according to an inventive aspect, this measure enablesto prevent or delay the electrodes from being reached by humity of theliquid subject to level detection, which with the passing of time isabsorbed by the overmoulded material that is in contact with the sameliquid.

Based on the aforesaid aspect of the invention, between the overmnouldedouter coating 30 and the electrodes J and J₁ of a respective array,there is set at least one intermediate layer made of an electricallyinsulating and substantially impermeabile material, which di differentfrom the material forming the coating 30, wherein the at least oneintermediate layer is obtained before overmoulding of the coating 30.

In preferred embodiments, the at least one intermediate layer betweenthe overnmoulded coating 30 and the electrodes J and J₁ comprises alayer of material including silicon (or its derivatives or compounds),i.e., a material that is practically insoluble in water and unattackableby acids. Among such materials of particular interest is, for example,silica, i.e., silicon oxide (silicon dioxide), which can provide animpermeable vitreous intermediate layer.

In view of the application proposed herein, preferred precursors forsynthesis of silica films or layers are silazanes, and in particularpolysilazanes, i.e., polymers the skeleton of which is constituted bysilicon atoms bridged by nitrogen atoms. Alternatively, for theapplication proposed herein, as precursors for the synthesis of silicafilms or layers other compounds could be used comprising silica (SiO₂),preferably in liquid or powder form, possibly in the form ofsilicon-dioxide or silica powder dispersed in a liquid, in particular inthe form designed to be deposited on a PCB and/or coat at least part ofthe PCB.

The length of the Si—N bond is in general estimated between 1.70 and1.75 Å, whereas the bond angle depends upon the silicon and nitrogensubstituent groups. On account of the polarity of the Si—N bonds and ofthe basicity of nitrogen, polysilazanes are particularly reactive inregard to hydrolysis in the presence of water (or protic solvents, suchas alcohols or acids). These reactions cause breaking of the bondbetween silicon and nitrogen and quickly lead to formation of silica andammonia. A particularly promising precursor in this sense isperhydropolysilazane (PHPS), which is constituted by silicon, nitrogen,and hydrogen and the structure of which resembles a three-dimensionallattice, where the silicon atoms are connected together via nitrogenbridges.

Perhydropolysilazane, like other polysilazanes, may be used, togetherwith at least one organic solvent and at least one catalyst, as base forobtaining liquid compositions that can be applied at room temperature ongeneric non-absorbant surfaces. Following upon application of such aliquid composition, a permanent barrier layer substantially made ofvitreous silica is formed, which chemically binds to the substrate atroom temperature and polymerises with the humidity present in the air.Compositions of this type are commercially available from variousmanufacturers and are traditionally used for protecting outer surfacesof means of transport or structures made of wood.

For the purposes of application of the aforesaid composition, thesubstrate of interest—here the PCB 20—must be previously cleaned, devoidof grease or oily substances, and dry. The application temperature ispreferentially comprised between +5° C. and +30° C., with a relativehumidity comprised between 30% and 80%. The solution may be applied onthe PCB 20 in the form of layer, for example via spraying or elsedipping the PCB itself in a container containing the liquid solution,i.e., using a dip-coating technique. Practically complete polymerisationmay be obtained at room temperature, usually after approximately 8 to 12h from application (completion of polymerisation occurs afterapproximately 7 days at room temperature). Not on the other handexcluded from the scope of the invention is a step of thermal treatmentto speed up polymerisation. After polymerisation, the layer applied istransparent, substantially having the appearance of a thin layer ofglass.

In addition, and/or as an alternative, the at least one intermediatelayer between the overmoulded coating 30 and the electrodes J and J₁ maycomprise a layer of composite material that includes silicon, or itsderivatives or compounds, for example, silicon oxide. A substantiallyimpermeable composite material of this type may have, for example, amatrix having a base of epoxy resin supplemented with glass-fibrefillers.

In various embodiments the at least one intermediate layer between theovermoulded coating 30 and the electrodes J and J₁ comprises at leasttwo different layers of material, each of which including silicon, orits derivatives or compounds. The aforesaid two layers may be two layersprevalently comprising vitreous silica, obtained starting from apolysilazane-based liquid solution, as referred to above. In otherembodiments, the at least one intermediate layer comprises a first layerof material including vitreous silica, obtained starting from apolysilazane as referred to above, and a second layer of compositematerial of the type referred to above, for example including glassfibre. In various preferential embodiments, the aforementioned secondlayer of composite material is in a position intermediate between thefirst layer of material and the electrodes J, J₁.

In other embodiments still, the at least one intermediate layercomprises at least two different layers of material, of which a firstintermediate layer including silicon, or its derivatives or compounds,and the other intermediate layer—on which the material of the coating 30is designed to be overmoulded—which is made of a polymer that is lessstiff, i.e., more flexible, than the material of the first layer, forexample a substantially impermeable polymer containing fluorinederivatives or compounds.

In various embodiments, the at least one intermediate layer comprises atleast one material or polymer that is at least in part flexible, ordeformable, or compressible, such as a fluoropolymer or an elastomer, onwhich the material of the coating 30 is designed to be overmoulded,where preferably the coating 30 is made of a polymer that is stifferthan the material of the aforementioned intermediate layer.

Between the overmopulded outer coating 30 and the electrodes J and/or J₁there may be set at least one intermediate layer made of an electricallyinsulating and substantially impermeable material that does not includesilicon or its compounds. In particularly advantageous embodiments, thismaterial is a polymer containing fluorine or its derivatives orcompounds, as described hereinafter. In other embodiments, the materialwithout silicon of the at least one intermediate layer is a layer thatcomprises an epoxy-based material, such as a layer of the type known as“solder-resist”, i.e., a thin layer of polymeric material designed toprovide a protection against oxidation, in particular an epoxy-basedmaterial. In the case where the material constituting the solder-resistor epoxy-based layer is similar to a paint or an ink, possibly of aphotosensitive type, it can be sprayed on or applied using silk-screenprinting techniques or the like; on the other hand, the solder-resist orepoxy-based layer may also be made in the form of a film applied using avacuum lamination method.

In the case exemplified in FIGS. 2-3, and in the corresponding FIGS.4-7, between the overmoulded outer coating 30 and the electrodes J andJ₁ of a respective array there are provided:

i) a first layer of composite material;

ii) a second layer of a material that is here assumed to be of asolder-resist or epoxy-based type; and

iii) a third, silica-based, layer.

In the case exemplified, the first layer of composite material has anepoxy-resin-based matrix that is filled with glass fibre. Veryadvantageously, the aforesaid first composite material may beconstituted by one of the layers of the multilayer structure itself ofthe PCB 20. With reference also to FIGS. 4-7, in the non-limitingexample illustrated, the supporting structure of the PCB 20 includes twolayers 20 ₁ on the outer face of which are set the correspondingelectrodes J and J₁, respectively. Preferably, but not necessarily,between the two layers 20 ₁ one or more further intermediate layers 20 ₂are provided (by the way, in other non-represented embodiments, theelectrodes J and J₁ might be even arranged on the opposite major facesof one and the same layer of the PCB 20). The layers 20 ₁ (or theopposite faces of the aforesaid one and the same layer) are in turncovered by respective outer layers 20 ₃ of the same multilayeredstructure, such that the electrodes J and J₁ are correspondinglycovered. Hence, in the example the layers 20 ₃ constitute the oppositemajor sides (20 a, FIG. 8) of the PCB 20. The various layers 20 ₁, 20 ₂and 20 ₃ of the PCB 20 are preferably formed with one same material, forinstance FR4 or the like, even if this is not an essential feature.

Once again with reference to the non-limiting example illustrated inFIGS. 2-7, on outer layers 20 ₃ of the multilayer structure of the PCB20 there are respective second layers 40, which are here assumed asbeing of a solder-resist or epoxy-based type, designated by 40. It willbe appreciated that, since the electrodes J and J₁ are arranged withinthe supporting structure of the PCB 20, the main function of the layers40, when these are of a solder-resist or epoxy-based type, is to counterpossible oxidative phenomena, and/or phenomena of infiltration ofhumidity and/or liquid, rather than preventing possible short-circuits.

In the example the layers 40 coat only the outer face of the layers 20 ₃of the PCB 20, preferably completely, but in other embodiments thelayers 40 may belong to a single coating that surrounds the PCB 20, orat least one portion thereof at its major sides and its lateral edges orminor sides (as for the layer or coating 50 described hereinafter).

Finally, present on the PCB 20, i.e., on each of the layers 40, is thethird layer substantially made of silica, designated by 50. The thirdlayer 50, or each third layer 50, may be applied as an individual layerthat coats a respective layer 40 or else, as in the case exemplified,may itself be applied as a coating that surrounds the PCB 20 on a numberof sides and edges. For this reason, in what follows, the layer 50 willalso be identified as “intermediate coating”. Also the intermediatecoating or layer 50 may surround or coat the entire PCB 20 or only apart of interest thereof.

By way of indication, the layers 20 ₃ of composite material may have athickness of between 0.2 mm and 0.4 mm, the layers 40 may have athickness of between 10 μm and 30 μm, and the intermediate coating 50(or at least its layer at the major sides of the PCB 20) may have athickness of between 10 μm and 30 μm. The overmoulded outer coating 30may have a thickness of between 1 mm and 2.4 mm, preferably of between1.4 mm and 1.8 mm, very preferably between 1.5 and 1.6 mm.

The layers made of composite material 20 ₃ are formed during productionof the PCB 20 itself, themselves constituting part of its multilayerstructure. As has been said, the multilayer structure of the PCB 20 maybe obtained using materials such as FR4, or vetronite or similarelectrically insulating composite materials, of a GRP (Glass-ReinforcedPlastic) type. The preferred composites used are epoxy-based, such as anepoxy resin with glass fibre. The various layers of the structure of thePCB are preferably laminated on one another, according to a technique inthemselves known in the sector of the manufacture of multilayer PCBs.

The layers 40 may be sprayed on the outer face of the layers 20 ₃ butthere is nothing in principle to rule out application of the epoxymaterial of the layers 40 in another way, for example via overmoulding.

Also the solution based on polysilazanes or silicon dioxide, which is tobe converted prevalently into silica, i.e., to provide a vitreousintermediate coating 50, may be deposited or applied using spray-coatingtechniques, or else may be applied by dipping the PCB totally orpartially in a container containing the liquid solution, i.e., usingdip-coating techniques. Deposition may, on the other hand, be carriedout using other known techniques, such as spin-coating (deposition byrotation of the PCB), flow-coating (deposition via a flow that impingesupon the PCB), CVD (Chemical Vapour Deposition), PVD (Physical VapourDeposition), etc. These techniques may also be used for deposition ofthe layers 40.

As may be seen, according to an inventive aspect, the level-sensordevice 10 may comprise four insulation elements or layers (30, 50, 40,20 ₃) that separate the electrodes J, J₁, i.e., the structure (20 ₁, 20₂) that supports them, from the liquid undergoing detection.

Exemplified in FIGS. 9-12 is a possible sequence for producing thecasing body of a device according to possible embodiments of theinvention. Illustrated in FIG. 9 is the semi-finished product—includingthe PCB 20, the layers 40, and the intermediate coating or layers50—designated as a whole by 20′. It is to be assumed that the aforesaidsemi-finished product 20′ is already provided, not only with theelectrodes J and J₁, but also with the remaining part of the detectionand/or processing circuitry. Applied to the semi-finished product 20′ isthe body part 21, for example shaped like a shell defining a cavitydesigned to receive at least partially the regions 25 and 26 of the PCB20 (FIG. 8), i.e., of the semi-finished product 20′. As has been said,preferentially the part 21 integrates the connector body 15 a and theterminals 17, with the latter that in this stage are electricallyconnected to corresponding conductive paths of the PCB 20.

Next (see FIG. 10), applied to the semi-finished product 20′ is the bodypart 23, which—for example—is also shaped like a shell bu defining herea cavity able to receive partially only the intermediate region 26 (FIG.8), such that the latter is enclosed between said part 23 and acorresponding portion of the part 21 (said corresponding portion may beconfigured as a component being distinct and coupled to the body part21). The two parts 21 and 23, in particular when they are both shapedlike a shell, may be provided with means for mutual coupling, such aspins and seats of the part 21 designed to couple with correspondingseats and pins of the part 23.

Preferentially, the body parts 21 and 23 are made of a polymer having amelting point higher than 260° C. or in any case designed to resist thistemperature in particular in order to be able to withstand possibleovermoulding of at least one polymer at a temperature lower than 250°C., in particular a polymer designed to provide the outer coating 30 ofthe casing body of the device 10. For this purpose, in variousembodiments, the material for the body parts 21 and 23 is selected frompolyphthalamide (PPA), polyamide copolymers (PA66), and polyphenylenesulphide (PPS).

Possibly, before overmoulding of the outer coating 30, at the cavitiesof the body parts 21, 23 and of the corresponding portions of thesemi-finished product 20′, i.e., of the PCB 20, that are housed in saidcavities, there may be applied a resin aimed at improving thecharacteristics of protection of the electrical and/or electroniccomponents that are located in these regions. The resin or similarmaterial used is preferably of the type with low melting point orpolymerisation temperature, in particular a temperature oftransformation such as not to damage the electrical and/or electroniccomponents (such as a temperature of between 180° C. and 240° C.,preferably close to 200° C.). A thermoplastic material suitable for thepurpose, which is preferably relatively elastic or not stiff, may be ofthe so-called hot-melt or hot-glue type.

Next, at least the portion of the PCB 20, i.e., of the semi-finishedproduct 20′, that includes the detection region 24 is inserted in amould for overmoulding the polymeric material that is to provide theouter coating 30. The material used for overmoulding of the coating 30may be a thermoplastic material or else a thermosetting material.Preferred materials are high-density polyethylene (HDPE), polypropylene(PP), polyphthalamide (PPA), and polyphenylene sulphide (PPS).

Preferentially, the mould is configured for receiving also at least partof the intermediate region 26, provided with the body parts 21 and 23.In this case, in the course of the overmoulding operation, the circuitcomponents possibly present in the intermediate region 26 of the PCB 20,i.e., of the semi-finished product 20′, albeit located within theovermoulding area, are in any case protected, in view of the fact thatthis intermediate region is enclosed between the body parts 21 and 23;the protection is further increased in the presence of the aforesaidresin.

The result of the operation of overmoulding of the coating 30 isexemplified in FIG. 11, where the casing body of the device is nowformed to a prevailing extent: as may be noted, the overmoulded coating30 defines at least the detection portion 14 of the casing body and,preferably, at least part of its mounting portion 16, the outside of thelatter being mainly obtained by the material moulded over the body part23 and the corresponding portion of the body part 23.

The casing body of the device 10 may be then completed by associating tothe semi-finished product of FIG. 11 one or more further body parts, inparticular with the aim of obtaining the corresponding connectionportion 15. To this purpose, by referring to FIG. 12, the body part 22is coupled to the body part 21, which is not covered by the material ofthe coating 30, with at least one portion of the control region 25 (FIG.8) of the PCB 20, i.e., of the semi-finished product 20′, set between.The body part 22 may be configured as a distinct component, for examplein the form of a shell fixed to the body part 21 (for example fixed bysnap-fitting, or via threaded means, or welded, or glued), or the bodypart 22 may be also configured and an overnoulded part.

Embodiments of the sort represented in FIGS. 2-7 are particularlyadvantageous in so far as they prevent the humidity absorbed by thematerial of the coating 30 from possibly reaching the electrodes J and eJ₁, or at least they considerably delay such humidity in reaching theelectrodes J and J₁. In this perspective, the solution enables topossibly use, in order to obtain the overmnoulded coating 30,thermoplastic material which are relatively cheaper and/or more easilymouldable, even if they have a lower resistance to humidityinfiltration.

In various embodiments, the layer or layers 40 are omitted. An examplein this sense is illustrated in FIGS. 13-16, where provided between theelectrodes J and J₁ of the respective array and the coating 30 are twolayers containing silicon or its derivatives or compounds, hererepresented by a layer 20 ₃ of the PCB 20 and by an intermediate coating50. In embodiments of the type illustrated in FIGS. 13-16, in any case,between the liquid undergoing level detection and the electrodes J andJ₁ are, in addition to the outer coating 30, two further layers ofdifferent materials (50 and 20 ₃). Insulation of the electrodes J and J₁from the humidity or liquid that could possibly impregnate the coating30, albeit reduced as compared to embodiments of the type exemplified inFIGS. 2-6, remains in any case high and more than sufficient for variousapplications of the device, for example for the use of somethermoplastic materials for obtaining the coating 3.

As may be seen, according to an inventive aspect, the level-sensordevice 10 comprises at least three insulation elements or layers (30,50, 40) that separate the electrodes J, J₁, i.e., the structure (20 ₁,20 ₂) that supports them, from the liquid undergoing detection.

In various embodiments, the electrodes J and/or J₁ are not arrangedwithin the structure of the PCB 20, but arranged at a respective outerface of said structure. An example in this sense is illustrated in FIGS.17-20. In the example illustrated in these figures the outer layers 20 ₃of the PCB 20 are hence not present, with the electrodes J and J₁ thatdirectly give out onto the outside of the PCB itself, in positioncorresponding to the opposite major sides thereof (here represented bythe layers 20 ₁ that carries the electrodes); however, as already said,the electrodes could be set on one side only of the PCB. It will beappreciated that, in embodiments of this sort, the PCB 20 does notnecessarily have a multilayer structure. In the case of FIGS. 17-20, thelayers 40, for example of a solder-resist or epoxy type, are present,applied directly on the layers 20 ₁ of the PCB 20 so as to cover alsothe electrodes J and J₁. In embodiments of the type in which thematerial necessary for formation of the layers 40 is in the form ofpaint or ink, this material may, if necessary, be applied—for example,via silk-screen deposition—in such a way that the outer surface of thelayers 40 is substantially plane, as in the case illustrated (i.e., thecorresponding material will be deposited in such a way that thethickness of the layers 40 is smaller in the area of the electrodes Jand J₁). This does not, however, constitute an essential characteristicfor the purposes of operation of the device.

Also in embodiments of the type illustrated in FIGS. 17-20, in any case,set between the liquid undergoing level detection and the electrodes Jand J₁ are—in addition to the outer coating 30—two further layers ofdifferent materials (40 and 50), and this enables to obtain theovermoulded coating 30 with thermoplastic materials which are cheaperand/or more easily workable in order to obtain a longitudinally extendedcoating, as required by the use proposed herein.

Also in this case, according to an inventive aspect, the level-sensordevice 10 comprises three insulation elements or layers (30, 50, 40)that separate the electrodes J, J₁, i.e., the structure (20 ₁, 20 ₂)that supports them, from the liquid undergoing detection.

In various embodiments, the intermediate coating or the layers 50 areomitted. An example in this sense is illustrated in FIGS. 21-24,according to which between the electrodes J and J₁ of the respectivearray and the coating 30 are two layers of different materials, hererepresented by a layer 20 ₃ of the PCB 20 and a layer 40, for example ofa solder-resist or epoxy-based type, are in any case provided. Hence,also in this case, set between the liquid undergoing level detection andthe electrodes J and J₁ are, in addition to the outer coating 30, twofurther layers of different materials (layers 40 and 20 ₃), whichprevents or in any case delays the electrodes from being reached by thehumidity which may impregnate with the passing of time the coating 30.

Hence, also in this case, the level-sensor device 10 comprises threeinsulation elements or layers (30, 40, 20 ₃) that separate theelectrodes J, J₁, i.e., the structure 20 ₁, 20 ₂ that supports them,from the liquid undergoing detection.

FIGS. 25-28 exemplify further possible embodiments, where the layers 40are omitted and the electrodes J and/or J₁ are not arranged within thestructure of the PCB 20, but in a position corresponding to a respectiveouter face of this structure. Hence, also in this case, the outer layers20 ₃ of the PCB 20 are absent, with the electrodes J and J₁ thatdirectly give out on the outside of the PCB, in positions correspondingto its two major opposite sides (also here represented by the layers 20₁ that carry the electrodes). The intermediate coating or the layers 50are thus applied directly on the layers 20 ₁ of the PCB 20 so as tocover also the electrodes J and J₁. It will be appreciated that, also inembodiments of this type, the PCB 20 does not necessarily have amultilayer structure. In embodiments of the type illustrated in FIGS.25-28 set between the liquid undergoing level detection and theelectrodes J and J₁ is, in addition to the coating 30, only thesilica-based intermediate coating or layer 50.

In this inventive configuration, the level sensor device 10 comprisestwo insulation element or layers (30, 50) which separate the electrodesJ, J₁, i.e., the structure 20 ₁, 20 ₂ supporting them, from the liquidundergoing detection.

The hygroscopic insulation thus obtained, albeit reduced as compared toother embodiments described previously, is in any case sufficient forvarious applications of the device, in particular when the material usedfor providing of the intermediate layer 50 is a vitreous or silica-basedlayer that uniformly coats the PCB 20, without leaving any passages orporosities, and hence with good sealing characteristics, even though ithas a small thickness.

FIGS. 29-32 exemplify further possible embodiments, where both thelayers 40 and the intermediate coating or layers 50 are omitted, withthe electrodes J and J₁ that are arranged within the multilayerstructure of the PCB 20, underneath the outer layers 20 ₃. Hence, alsoin embodiments of this type, set between the liquid undergoing leveldetection and the electrodes J or J₁ is, in addition to the outercoating 30, just one layer 20 ₃ belonging to the multilayer structure ofthe PCB 20. Also structures of this type are sufficient for protectionor at least for delaying the negative effects of possible absorption ofhumidity or liquid by the material used for obtaining the overmouldedcoating 30.

Also in this inventive configuration, the level sensor device 10comprises two insulation element or layers (30, 20 ₃) which separate theelectrodes J, J₁, i.e., the structure 20 ₁, 20 ₂ supporting them, fromthe liquid undergoing detection.

Likewise, FIGS. 33-36 exemplify further possible embodiments, where theintermediate coating or layers 50 are omitted, and the electrodes J andJ₁ are not arranged within the structure of the PCB 20, but in aposition corresponding to a respective outer face of the structure.Hence, also in this case, no outer layers 20 ₃ of the PCB 20 is present,but laid on the layers 20 ₁ that carry the electrodes J and J₁ areapplied respective layers 40, for example of a solder-resist orepoxy-based type, so as to cover the electrodes themselves. It will beappreciated that, also in embodiments of this type, the PCB 20 does notnecessarily have a multilayer structure. In embodiments of this type,set between the liquid undergoing level detection and the electrodes Jor J₁ is, in addition to the outer coating 30, just the layer 40, whichis in any case sufficient in various applications.

Also in this inventive configuration, the level sensor device 10comprises two insulation element or layers (30, 40) which separate theelectrodes J, J₁, i.e., the structure 20 ₁, 20 ₂ supporting them, fromthe liquid undergoing detection.

Provision of an intermediate coating or layers 50 prevalently made ofsilica obtained starting from a polysilazane-based composition isparticularly advantageous also because, during the correspondingpolymerisation, the silicon binds to the —OH group of the correspondingsubstrate 20, and/or 40. In this way a bond tendentially of a secondarytype is obtained between the intermediate coating 50 and the underlyingsubstrate (which, according to the cases, is constituted by a layer 40or a layer 20 ₃) which contributes to improving fixing between thematerials and hence the strength of the structure. In this perspective,as mentioned previously, in various embodiments, the PCB 20 and/or thelayers 40 are preferentially formed using an epoxy-based material, i.e.,one comprising an —OH group, thereby guaranteeing a chemical bond withthe intermediate coating 50 and/or the layers 40. Once again in thisperspective, the electrodes J and J₁ are preferably made of a metal ormetal alloys (for example, copper or copper-based alloys). Given that inthe production stage on the aforesaid metal there occur in any casepseudo-oxidation processes with grafting of —OH functional groups, alsoin the cases where the polysilazane-based or silicon-dioxide-basedsolution is applied partially in contact with the electrodes J, basicchemical bonds (—OH or else O* functional groups) form between the metaland the polysilazanes or silicon dioxide, with consequent advantages interms of fixing between the different materials.

In various particularly advantageous embodiments, the epoxy-based layersdesignated previously by 40 may be substituted by layers 40′ made of apolymer containing precursors, or derivatives, or compounds of fluorinesuch as a fluorinated polymer or fluoropolymer or perfluorinatedpolymer, preferably without perfluorooctane sulphonate (PFOS) andperfluorooctanoic acid (PFOA). For this reason, in various ones of thefigures mentioned above, associated to the reference number 40 is alsothe reference number 40′ in brackets. Preferred materials are, forexample, fluorinated ethylene propylene (FEP), polytetrafluorineethylene (PTFE) and, more in general, fluorine-acrylate-based polymers.The configurations described previously, where the layers 40 areenvisaged are hence to be understood as valid in the case where theselayers are substituted by layers 40′ made of a polymer containingprecursors or derivatives or composites of fluorine. Also the layers 40′may belong to an intermediate coating that surrounds the PCB 20, i.e.,that extends also at the edges or minor sides of the PCB (asillustrated, for example, in FIGS. 37-46). The layers or coatings 40′may have a thickness of between 10 μm and 70 μm.

The studies conducted by the present Applicant have made it possible toascertain that fluorine-based polymeric materials, or derivatives orcompounds of fluorine (such as completely or partially fluorinatedfluoropolymers), are particularly advantageous for the purposes of theapplication proposed herein. Fluorates, in addition to being chemicallyvery resistant, present an excellent resistance also at hightemperatures, and are thus perfectly suitable for withstandingovermoulding of the coating 30. These materials are moreover relativelyflexible, or not stiff, and relatively deformable or compressible, andare hence able to withstand very well thermal expansion and thermalshock, likewise presenting very low coefficients of friction, with aconsequent possibility of withstanding the relative movements that, onaccount of different coefficients of thermal expansion, may occurbetween the overmoulded material of the coating 30 and the PCB 20(and/or possible other layers, such as the layers 40 and/or 50).

Practical permeation tests conducted by the present Applicant have alsomade it possible to ascertain that fluorinated polymers enable excellentresults to be obtained in terms of resistance to water-urea solutions,such as AdBlue, this also by virtue of the very low surface energy ofthe fluorinated polymers, which are highly hydrophobic. Thischaracteristic is particularly advantageous in the case where the liquidof which the level is be detected is water or a water-based solution(such as AdBlue, which prevalently consists of water).

The presence of an intermediate layer 40′ made of fluorinated polymermoreover enables good protection against chemical aggression of theelectrodes, and/or of the PCB 20, in the case of any infiltration ofwater-urea solutions through the coating 30.

The use of fluoropolymers for producing layers or coatings 40′ isparticularly advantageous also in view of the fact that, in variousconfigurations, during polymerisation of the material, it is possible toobtain chemical and/or structural bonds with the materials of thecorresponding substrate. This is particularly advantageous when the PCB20 and/or the layers 40 are made of epoxy-based materials. In thisperspective, as already mentioned, the material for the PCB 20 ispreferentially epoxy-based (for example FR4, the matrix of which is ingeneral constituted by an epoxy resin), and the layers 40 of asolder-resist type are also made of an epoxy resin.

For instance, illustrated in FIGS. 37-40 is the case where between theovermoulded outer coating 30 and the electrodes J and J₁ of a respectivearray there are provided:

i) a first layer of composite material 20 ₃;

ii) a second layer of material 40; and

iii) a third layer 40′ with a fluorinated-polymer base;

According to embodiments (not illustrated), the layer of compositematerial 20 ₃ may be omitted.

In the case exemplified in the figure, the possible first layer ofcomposite material is constituted by an outer layer 20 ₃ of themultilayer structure of the PCB so that the electrodes J are coatedaccordingly, whereas the layer 40 belongs to an intermediate coating ofa solder-resist or epoxy-based type, which coats the structure of thePCB 20 at its major sides and its edges or minor sides. The third layer40′ belongs, instead, to an outer fluorinated-polymer intermediatecoating, for example made of FEP, which surrounds the epoxy-basedcoating to which the layers 40 belong. The material of the outer coating30 is then overmoulded on the coating to which the layers 40′ belong(however, as said, this is not an essential feature, provided that thecoating may be obtained separately and then mounted the on the PCB 20,i.e., the semi-finished product 20′).

In solutions of the type exemplified in FIGS. 37-40, provided betweenthe layers or coating 40′ and the layers or coating 40 is a hydrogenbond between the —OH group of the epoxy-based substrate, hererepresented by the layers or coating 40, with the more electronegativeatoms of the fluorine of the fluorinated polymer, for example the FEP,that provides the layers or coating 40′. The hydrogen bond or hydrogenbridge is a particular case of intermolecular force implicated in whichis a hydrogen atom involved in a covalent bond with very electronegativeelements (such as fluorine, oxygen, or nitrogen), which attract tothemselves the valence electrons, acquiring a partial negative charge(δ−), leaving the hydrogen with a partial positive charge (δ+).Simultaneously, the hydrogen is attracted by an electronegative atom ofa nearby molecule.

It will thus be appreciated that the aforesaid bond contributes toimproving fixing between the materials, and hence to the strength of thestructure. Bonds similar to the ones just exemplified are formed whenlayers or coatings of the type designated by 40′ are applied directly ona PCB 20 made at least in part of an epoxy resin. Cases of this type areexemplified in FIGS. 41 and 42. FIG. 41 regards the case of a coating40′ that coats a multilayer PCB 20, where the electrodes J and/or J₁ arealready covered with a layer made of composite 20 ₃, whereas FIG. 42regards the case of a PCB with electrodes J exposed (i.e., on the outerfaces of the layers 20 ₁).

According to one aspect, the present invention proposes elimination orat least reduction of possible mechanical stresses to which internalelements of the level-sensor device may be subjected (such as the PCB20, and/or circuit components carried by the PCB, and/or intermediatelayers of material between the PCB and the outer coating), due forexample to shrinkage of the overmoulding material of the outer coating30 and/or deformations due to external pressures of thrusts by thefrozen liquid and/or following upon dimensional variations due tothermal jumps or shocks (for example, following upon heating of thefrozen liquid, and/or variations of the ambient temperature).

For this reason, in embodiments in themselves inventive, and as alreadymentioned previously, at least one intermediate layer of the deviceperforms functions of mechanical compensation and comprises for thispurpose a material or polymer that is at least in part flexible, ordeformable, or compressible, on which there is to be overmoulded thematerial of the coating 30, where preferably the coating 30 is made of apolymer that is stiffer than the material of the aforementionedcompensation intermediate layer.

For instance, as mentioned previously, fluoropolymers are relativelyflexible, and/or deformable, and distinguished by low surface frictionso that the corresponding layers can advantageously perform functions ofmechanical compensation, for instance, in order to absorb possiblemechanical stresses determined by the coating 30 with respect to anunderlying substrate, such as the PCB 20 or the coating 40. As has beensaid, these mechanical stresses may be due to shrinkage of the outercoating 30 and/or to stresses on the sensor device induced by the frozenliquid or frozen parts thereof, and/or following upon thermal shock thatinduces dimensional variations of parts of the device.

In other embodiments, the aforementioned functions of compensation ofthe aforesaid possible stresses may be obtained by means of one or morelayers 40′ made of relatively elastic, and/or compressible, and/ordeformable elastomers or polymers different from the ones referred topreviously, even ones not containing fluorine derivatives or compounds.

In particularly advantageous embodiments of the invention, it is alsopossible to combine an intermediate layer or coating of the typedesignated previously by 50, which is relatively more rigid and brittleand hence potentially subject to the risk of cracking following uponmechanical deformations or strains, with a fluorinated layer or coatingthat coats the first layer 50, so as to prevent excessive shrinkageand/or deformations during the settling step of the overmoulded materialof the coating.

Such a case is exemplified in FIGS. 43-46, where applied to a multilayerPCB 20 is an intermediate coating 50 made of silica or silicon oxide, ofthe type described previously, on which an intermediate coating 40′,made of a fluoropolymer, is in turn applied. It will be appreciated thatsolutions of this sort enable maximisation of insulation of theelectrodes J and/or J₁ in regard to humidity and/or liquid that mayimpregnate the overmoulded material of the oputer coating.

It should moreover be emphasised that the higher flexibility (oryielding, or compressibility, or deformability) of a coating made of afluoropolymer as compared to corresponding substrates of a vitreous type(50), or composite type (20), or epoxy type (20, 40) protects the latterfrom mechanical strains, deformation and stresses which may originateduring freezing of the liquid undergoing detection and due to possibleimpacts with ice pieces formed in said liquid.

In general, the functions of mechanical compensation described abovewith reference to FIGS. 37-42 hence also apply in the case exemplifiedin FIGS. 43-46, in particular in order to safeguard the integrity of thevitreous coating 50.

From the foregoing description the characteristics of the presentinvention emerge clearly, as do its advantages, mainly represented bythe simplicity of construction of the level-sensor device proposed, itscontained cost, and its precision and reliability.

It is clear that numerous variants may be made by the person skilled inthe branch to the devices and methods described herein purely by way ofexample, without thereby departing from the scope of the invention asdefined by the annexed claims.

As indicated previously, presence of two arrays of electrodes, each onein a position corresponding to one side of the PCB 20, does notconstitute an essential characteristic of the device 10, which may beprovided with just the electrodes J or just the electrodes J₁. Hence, inthe devices 10 of this type, the number of intermediate between theouter coating 30 and the electrodes J or J₁ may be correspondinglyreduced, for example by exploiting just one of the outermost layers 20 ₃of the PCB 20 for the purposes of the invention and/or by providing justone layer 40 (and/or 40′) and/or at the side of interest of the PCB 20.By the way, also in the case of a device 10 provided with a single arrayof electrodes J or J₁, the insulating structure may comprise layers 40(and/or 40′), and/or 50 also on the side of the PCB where thelevel-detection electrodes are not present.

The PCB of the sensor device according to the invention does notnecessarily have to be made using an epoxy-based material or a materialincluding silicon or its derivatives or compounds. In possible variantembodiments, the PCB 20—even one not having a multilayer structure—maybe obtained using, for example, a fluorinated polymer or PTFE, or apolyimide, or ceramic materials.

The invention has been described with particular reference to detectionof the level of a liquid medium, in particular water or aurea-and-water-based additive, but as already mentioned the sensordescribed can be used in combination with different substances andmaterials, even ones potentially subject to solidification by freezing.

In some applications, it is possible for a level measurement withdifferent areas of detection to be required, each of which has adifferent measurement resolution and which are located in differentpositions of the detection part 11 of the device 10. This need leads,for example, to positioning electrodes having different geometries—interms of shape and size—along the detection region 24 of the PCB 20 inorder to guarantee the resolution or tolerance of measurement requiredin the given area. This choice is in some cases limited by the need tominimise the cost of the control electronics of the device, and inparticular of a controller thereof (which is linked to the number of itsinputs and hence to the number of electrodes that it is able to manage).For this reason, in some applications, it may prove convenient toincrease the size of the electrodes in the areas where maximumresolution of detection is not necessary (typically at the two ends). Inthis perspective, according to possible variant embodiments, the arrayor arrays of capacitive elements provided in a position corresponding toa major face, or each major face, of the PCB 20, in its detection region24, may comprise a number of series of electrodes J or J₁ diversifiedfrom one another in terms of shapes and/or size.

Individual characteristics described with reference to embodimentsdescribed previously may be combined with one another in otherembodiments.

Reference has previously been made to functions of mechanicalcompensation performed by one or more intermediate layers or coatings,which are, for example, made of materials with a base of fluorinederivatives or compounds, or else of elastomers not necessarilyincluding fluorine derivatives or compounds. Layers or coatings of thistype, owing to their elastic and/or compliant nature may extend or beprovided also in regions of the circuit support different from thedetection region, such as the regions 25 and/or 26, in particular inorder to coat and protect possible electrical and/or electroniccomponents mounted in an exposed position on a circuit support orsubstrate, such as the PCB 20.

As has been mentioned, on the circuit support of the device according tothe invention there may be provided at least one temperature sensor,which, like the electrodes J and/or J₁, may be insulated from the liquidundergoing level detection by at least two layers of material (30, 50,40, 40′, 20 ₃).

The invention claimed is:
 1. A capacitive level sensor device, fordetecting the level of a medium contained in a container, wherein thedevice comprises a circuit support, which extends longitudinallysubstantially according to level-detection axis, the circuit supporthaving a first longitudinal end and a second longitudinal end, thecircuit support having a supporting structure which includes a firstlongitudinal major side and a second longitudinal major side opposite toone another, and two opposite longitudinal minor sides each extendingbetween the first and second longitudinal major sides, wherein thecircuit support has, in a detection region thereof that includes saidfirst longitudinal end, at least one first plurality of first capacitiveelements, which comprise at least one first array of first electrodesspaced from one another along the level-detection axis, the firstelectrodes being made of an electrically conductive material andarranged at least in part in a position corresponding to at least thefirst longitudinal major side of the supporting structure of the circuitsupport, wherein the device has a casing body which comprises anelectrically insulating and fluid-tight detection portion, which coversthe detection region of the circuit support, the detection portion ofthe casing body having an outer surface which include a firstlongitudinal major surface and a second longitudinal major surfaceopposite to one another, and two opposite longitudinal minor surfaceseach extending between the first and second longitudinal major surfaces,wherein the first electrodes each have a front major face and a backmajor face opposite to one another, the front major face of the firstelectrodes being closer to the first longitudinal major surface of thedetection portion of the casing body, and the back major face of thefirst electrodes being farther from the first longitudinal major surfaceof the detection portion of the casing body, wherein the detectionportion of the casing body comprises an overmoulded outer coating, madeof a first electrically insulating polymeric material, the firstelectrically insulating polymeric material defining the outer surface ofthe detection portion of the casing body which is designed to be incontact with the medium the level of which has to be detected, whereinbetween at least part of the overmoulded outer coating and the frontmajor faces of the first electrodes there is set at least oneintermediate layer made of an electrically insulating material differentfrom the first electrically insulating polymeric material, and whereinthe at least one intermediate layer comprises a layer made of a materialselected from among materials that include silicon, or derivatives orcompounds thereof, or materials that include fluorine derivatives orcompounds.
 2. The device according to claim 1, wherein the at least oneintermediate layer comprises at least one layer substantially made ofsilicon oxide.
 3. The device according to claim 2, wherein the at leastone layer substantially made of silicon oxide is formed starting from acomposition including a silazane, or a polysilazane, or aperhydropolysilazane.
 4. The device according to claim 2, wherein the atleast one intermediate layer moreover comprises at least one layer ofmaterial belonging to the supporting structure of the circuit support.5. A capacitive level sensor device, for detecting the level of a mediumcontained in a container, wherein the device comprises a circuitsupport, which extends longitudinally substantially according tolevel-detection axis, the circuit support having a first longitudinalend and a second longitudinal end, the circuit support having asupporting structure, wherein the circuit support has, in a detectionregion thereof that includes said first longitudinal end, at least onefirst plurality of first capacitive elements, which comprise at leastone first array of first electrodes, the first electrodes being made ofan electrically conductive material and arranged at least in part in aposition corresponding to at least one first side of the supportingstructure of the circuit support, wherein the device has a casing bodywhich comprises an electrically insulating and fluid-tight detectionportion, which covers the detection region of the circuit support,wherein the detection portion of the casing body comprises anovermoulded outer coating, made of a first electrically insulatingpolymeric material, the first electrically insulating polymeric materialdefining an outer surface of the casing body which is designed to be incontact with the medium the level of which has to be detected, whereinbetween at least part of the overmoulded outer coating and the firstelectrodes there is set at least one intermediate layer made of anelectrically insulating material different from the first electricallyinsulating polymeric material, wherein the at least one intermediatelayer comprises at least one layer substantially made of silicon oxideand at least one layer of material belonging to the supporting structureof the circuit support, the at least one layer of material belonging tothe supporting structure of the circuit support being in a positionintermediate to the first electrodes and the at least one layersubstantially made of silicon oxide.
 6. The device according to claim 1,wherein the at least one intermediate layer comprises at least one layerincluding a fluoropolymer.
 7. The device according to claim 1, whereinthe at least one intermediate layer comprises at least one layer made ofa material that includes silicon, or derivatives or compounds thereof,and at least one layer made of a material that includes fluorinederivatives or compounds.
 8. A capacitive level sensor device, fordetecting the level of a medium contained in a container, wherein thedevice comprises a circuit support, which extends longitudinallysubstantially according to level-detection axis, the circuit supporthaving a first longitudinal end and a second longitudinal end, thecircuit support having a supporting structure, wherein the circuitsupport has, in a detection region thereof that includes said firstlongitudinal end, at least one first plurality of first capacitiveelements, which comprise at least one first array of first electrodes,the first electrodes being made of an electrically conductive materialand arranged at least in part in a position corresponding to at leastone first side of the supporting structure of the circuit support,wherein the device has a casing body which comprises an electricallyinsulating and fluid-tight detection portion, which covers the detectionregion of the circuit support, wherein the detection portion of thecasing body comprises an overmoulded outer coating, made of a firstelectrically insulating polymeric material, the first electricallyinsulating polymeric material defining an outer surface of the casingbody which is designed to be in contact with the medium the level ofwhich has to be detected, wherein between at least part of theovermoulded outer coating and the first electrodes there is set at leastone intermediate layer made of an electrically insulating materialdifferent from the first electrically insulating polymeric material,wherein the at least one intermediate layer comprises at least one layerincluding a fluoropolymer and at least one layer of material belongingto the supporting structure of the circuit support, the at least onelayer of material belonging to the supporting structure of the circuitsupport being in a position intermediate to the first electrodes and theat least one layer including a fluoropolymer.
 9. The device according toclaim 1, wherein the at least one intermediate layer moreover comprisesat least one layer made of an epoxy-based material.
 10. The deviceaccording to claim 1, wherein the supporting structure of the circuitsupport is formed at least in part with an epoxy-based material.
 11. Thedevice according to claim 10, wherein the epoxy-based material comprisesa composite material that includes glass-fibres in an epoxy resinmatrix.
 12. The device according to claim 1, wherein the circuit supporthas a multilayer supporting structure which comprises a plurality oflayers of electrically insulating material, the first electrodes beingset between two layers of electrically insulating material of themultilayer supporting structure.
 13. The device according to claim 1,wherein the circuit support has, in the detection region thereof, atleast one second plurality of capacitive elements that comprise a secondarray of second electrodes spaced from one another along thelevel-detection axis, the second electrodes being made of anelectrically conductive material and arranged at least in part in aposition corresponding to the second longitudinal major side of thesupporting structure of the circuit support, and wherein the secondelectrodes each have a front major face and a back major face oppositeto one another, the front major face of the second electrodes beingcloser to the second longitudinal major surface of the detection portionof the casing body, and the back major face of the second electrodesbeing farther from the second longitudinal major surface of thedetection portion of the casing body.
 14. The device according to claim13, wherein also between the overmoulded outer covering and the firstmajor front faces of the second electrodes there is set one said atleast one intermediate layer made of an electrically insulating materialdifferent from the first electrically insulating polymeric material. 15.A method for obtaining a capacitive level sensor device, to detect thelevel of a medium contained in a container, the method comprising thesteps of: i) providing a circuit support of an electrically insulatingmaterial which extends longitudinally substantially according to alevel-detection axis and which is provided, in a detection regionthereof, with a plurality of capacitive elements that include at leastone array of electrodes made of an electrically conductive material andspaced from one another along the level-detection axis, ii) coveringwith an electrically-insulating and fluid-tight material at least thedetection region of the circuit support, wherein step i) comprisesproviding the circuit support with a supporting structure having a firstlongitudinal major side and a second longitudinal major side opposite toone another, and two opposite longitudinal minor sides each extendingbetween the first and second longitudinal major sides, and providing theelectrodes with a front major face and a back major face opposite to oneanother, the electrodes being arranged at least in part in a positioncorresponding to at least the first longitudinal major side of thesupporting structure of the circuit support, wherein step ii) comprisesthe operation of forming an overmoulded outer covering with a firstelectrically insulating material, which defines an outer surface of adetection portion of a casing body of the device that is designed to bein contact with the medium the level of which has to be detected, theouter surface of the detection portion having a first longitudinal majorsurface and a second longitudinal major surface opposite to one another,and two opposite longitudinal minor surfaces each extending between thefirst and second longitudinal major surfaces, wherein step ii) comprisesforming the overmoulded outer covering such that the detection portionof the casing body covers the detection region of the circuit support,with the first longitudinal major surface of the detection portion ofthe casing body which is closer to the front major faces of theelectrodes, and with the back major faces of the first electrodes whichis farther from the first longitudinal major surface of the detectionportion of the casing body, wherein, before step ii), at least oneintermediate layer is set on the circuit support, the at least oneintermediate layer being formed with an electrically insulating materialwhich is different from the first electrically insulating material andwhich is selected from among materials that include silicon, orderivatives or compounds thereof, or fluorine derivatives or compounds,and wherein step ii) also comprises moulding the overmoulded outercovering directly over the at least one intermediate layer.
 16. Thedevice according to claim 1, wherein the first electrically insulatingpolymeric material is selected from among thermoplastic polymers orthermosetting polymers.